1960s IWC Cal 8531 - Reference help

My first post here and hoping I might be able to seek any information on an IWC cal. 8531 from the early 1960s. I bought this watch from a Swiss dealer last year, as I've long admired IWC from this period and wanted to add one to my collection. There is no model ref no on the caseback, only a serial number as you can see from the photos. Confusingly, I have seen both 309 and 809 references that appear similar to this example, but I would like to know if IWC watches from this era sometimes don't have reference numbers. Its a beautiful watch, so any information would add to my knowledge and appreciation - so any thoughts would be much appreciated.

Kind regards

Dan

Hello DANT

Congratulations to your beautiful IWC piece.

I would go to the IWC BTQ near by https://stores.iwc.com/ and request a service or a certificate of origin.

You also find on https://www.iwc.com/us/en/services/service-price-calculator.html a contact number on "I don't have my engraved serial number" for next steps.

Best

Andreas

Thank you, that's very helpful and much appreciated. Its interesting to know that IWC watches with this calibre didn't always have reference numbers. 

I'm grateful for your help and advice

Dan

Thank you Andreas, I appreciate your advice and comments - thank you for taking the time to reply

They always had ref nmbrs..just not always highlighted.

Ref 802 ( mk1 case)